Hydrological and Biogeochemical Cycling Along the Greenland Ice Sheet Margin

Maya Bhatia, Ph.D., 2012Sarah Das and Elizabeth Kujawinski, Advisors

Runoff from the Greenland ice sheet (GrIS) exports fresh water and sediment to the surrounding North Atlantic and Arctic Oceans. Snow and ice-melt on the ice sheet surface drains to the base (subglacial) where it becomes chemically enriched. I examine the interdependence of glacial hydrology and biogeochemical cycling in terms of export of carbon and iron. I develop an isotope mixing-model to quantify water sources to the bulk discharge draining a GrIS glacier. Results illustrate the seasonal evolution of the subglacial drainage network from a delayed-flow to a quick-flow system, and provide the necessary hydrological context to interpret and quantify glacially-derived organic carbon and iron fluxes. I combine bulk- and molecular-level studies of subglacial organic carbon to show that GrIS discharge exports old, labile organic matter. Similar investigations of dissolved and particulate iron reveal that GrIS discharge may be a significant flux of labile iron to the North Atlantic Ocean. Both carbon and iron undergo proglacial processing prior to export to the marine environment, and exhibit seasonal variability in correlation with subglacial drainage evolution. Collectively, this thesis provides some of the first descriptions and flux estimates of carbon and iron, key elements in ocean biogeochemical cycles, in GrIS meltwater runoff.